Intervertebral implant

ABSTRACT

The intervertebral implant is in the form of a three-dimensional structure ( 10 ) comprising (a) a top side ( 1 ) and an underside ( 2 ) which are designed to rest against the end plates of two adjacent vertebras, (b) a left side face ( 3 ) and a right side face ( 4 ), (c) a front face ( 5 ) and a rear face ( 6 ), (d) a horizontal center plane situated between the top side ( 1 ) and the underside ( 2 ), (e) a vertical center plane ( 8 ) situated between the left side face ( 3 ) and the right side face ( 8 ) and (f) a plurality of boreholes ( 9 ) passing through the implant structure ( 10 ) that are designed to receive longitudinal affixation elements ( 20 ), the axes ( 19 ) of said elements intersecting the horizontal center plane ( 7 ). At least one of the boreholes ( 9 ) is designed in a manner that the affixation element ( 10 ) received in it can be rigidly connected to the intervertebral implant. Said connection is implemented using a thread or by matching conical surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior patent application Ser. No. 10/923,534, filed Aug. 19, 2004, which is a continuation of International Application No. PCT/CH02/00099, filed Feb. 19, 2002. The entire contents of these applications are expressly incorporated herein by reference thereto.

FIELD OF THE INVENTION

The present invention relates to an intervertebral implant.

BACKGROUND OF THE INVENTION

Such an intervertebral implant is known from the British patent document 2,207,607 A which discloses a horseshoe implant structure having a plurality of cylindrical holes. These holes are fitted with inner, smooth surfaces and comprise only one stop for the heads of the bone screws to be inserted into them. This design incurs the drawback that the inserted affixation screws may be anchored into the bone only by their shanks, a rigid connection with the horseshoe shaped intervertebral implant being lacking. As soon as the anchoring of the bone screw in the bone is weakened, the intervertebral implant becomes displaceable relative to the screw and the bone screws may then migrate while endangering the blood vessels. Moreover the loosening of the intervertebral implant may entail pseudoarthrosis.

The above cited state of the art is intended merely to elucidate the background of the present invention but it does imply that the cited state of the art had actually been made public or was publicly known at the time of this application or at the time of its priority.

SUMMARY OF THE INVENTION

The objective of the present invention is palliation. This invention creates an intervertebral implant which is able to rigidly connect to bone affixation means in a manner that even in the event of bone structure weakening, loosening between the intervertebral implant and the bone affixation means shall be precluded.

The above problem is solved in the present invention by an intervertebral implant exhibiting the features of claim 1.

The advantages offered by the present invention substantially are attained by the rigid, that is by the firm connection between the intervertebral implant and the longitudinal affixing elements. Basically two different embodiment modes are available to attain said rigid connection.

In a first embodiment mode, at least one of the boreholes shall be internally threaded. In this case a matching bone screw fitted with a thread head may be rigidly screwed into the implant.

As regards a second embodiment mode, a front plate is mounted at the front surface of the three dimensional (3D) implant structure so as to be configured vertically to the horizontal center plane of the intervertebral implant, said boreholes passing through said front plate and receiving the anchored longitudinal affixation elements. Compared to the state of the art of a two-part implant, wherein a front plate is implanted in a separate operational step, the above design of the present invention offers the advantage that the intervertebral implant shall be implanted in a single step and hence in a simple and quicker manner. The invention offers a further advantage in that the intervertebral implant shall be affixed as frontally to the vertebra as possible, namely at a place where good bone material may be expected to be. As a result anterior displacement is restricted without thereby incurring greater danger to the surrounding structures than when using a state of the art intervertebral implant. The load still is being borne by the compressed vertebral implant, not by the front plate or the affixation screws.

In yet another embodiment mode of the present invention, the front plate is displaceably configured in the 3D implant structure in order that it may move vertically relative to this 3D implant structure. “Stress shielding” is attained in this manner (namely protection from or neutralization of mechanical stresses), and as a result the end plates may gradually match the intervertebral implant during the healing process.

As regards a further embodiment, the front plate is made of a material different from that of the 3D implant structure.

As regards a further embodiment of the present invention, at least one borehole tapers conically towards its underside and as a result a bone screw fitted with a matching conical head may be rigidly anchored in said borehole. Preferably the conical borehole exhibits a cone angle smaller than the resultant angle of friction. Appropriately the borehole's conicity shall be 1:3.75 to 1:20, preferably 1:5 to 1:15.

As regards a further embodiment mode of the present invention, the intervertebral implant side faces shall all be substantially convex.

Appropriately the intervertebral implant's top and/or undersides are not planar but convex. In this manner better matching to the end plates of the adjacent vertebras may be attained.

The boreholes preferably shall not pass through the left and right intervertebral implant side faces. Preferably again no borehole shall run through the front surface.

As regards a further preferred embodiment mode of the present invention, at least two boreholes shall be mutually parallel. This features facilitates inserting the vertebral implant during implantation.

As regards another preferred embodiment mode of the present invention, at least two boreholes shall run in mutually divergent manner as seen from the front side. As a result the bone screws shall move into a vertebral region offering better bone quality than found at the vertebra's center. Appropriately the borehole axes subtend an angle of 25° to 70°, preferably 35° to 55° with the horizontal center plane. This feature offers improved access for screw insertion.

As regards a further embodiment mode of the present invention, the boreholes shall not cross the horizontal center plane.

Depending on circumstance, two, three, four or even more longitudinal affixation elements may rigidly connected to the intervertebral implant; appropriately at least one affixation element shall pass through the top side and at least one affixation element shall pass through the intervertebral implant side.

Preferably the longitudinal affixation elements shall be bone screws comprising a head and a shank, said head preferably being fitted with an external thread that matches the inner thread of the intervertebral implant's borehole. As regards a second appropriate connection, preferably a bone screw shall be used of which the head tapers conically in the direction of the shank, the head's conicity corresponding to that of the intervertebral implant's borehole.

Regarding a further embodiment mode, at least two longitudinal affixation elements pass through the top side and at least two longitudinal affixation elements pass through the underside. In this manner the intervertebral implant is optimally anchored into the adjacent vertebras.

Preferably the screw-shaped longitudinal affixation elements exhibit a self-boring and self-tapping external thread. The longitudinal affixation elements also may be designed as unthreaded cylindrical pins fitted with a boring tip, preferably in the form of a trocar.

In another embodiment variation, the longitudinal affixation elements are spiral springs; lastly said longitudinal affixation elements also may be designed as single or multi-wing spiral blades.

In a further embodiment mode of the present invention, the longitudinal affixation element tip may be anchored in the structure of the intervertebral implant, as a result of which the head of the longitudinal affixation element may be anchored in the adjacent vertebra.

In a further embodiment mode of the present invention, the longitudinal affixation element head exhibits a widened diameter; also a support disk is provided for said head to rest against the vertebra.

The intervertebral implant may be made of any physiologically compatible material, though appropriately the implant structure shall consist of a physiologically compatible plastic, preferably an unreinforced plastic. The advantage offered by the invention over the already known, fiber-reinforced plastics used in implantology is that no reinforcing fibers will be bared—an eventuality that would be clinically disadvantageous. Appropriately bone screws consisting of non-reinforced plastic of which the external threads exhibit load bevels of 11° to 14°, preferably 12° to 13°, may be used in such an implant structure. The relatively small slope of the load bevel implements high clamping forces, as a result of which radial elongation and danger of cracking of the plastic are reduced. Appropriately the bone screws' external thread exhibits the bones at an angular pitch of 6° to 10°, preferably 7° to 9°. This particular angular pitch produces thread self-locking and prevents the bone screw from loosening on its own.

The borehole may be in the form of a metal bush fitted with an inner thread for the purpose of improving anchoring the bone screw in the plastic implant structure. The intervertebral implant also may consist partly of plastic and, in the borehole zones, of metal. This design offers improved guidance and anchoring of the bone screw in the intervertebral implant.

As regards a further preferred embodiment mode, the inside borehole walls are smooth, the thread head of a metallic, longitudinal affixation element cutting or tapping into said smooth wall.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and further embodiment modes of it are elucidated below in relation to the partly schematic representation of two illustrative embodiments.

FIG. 1 is a perspective view including a partial section of the intervertebral implant with inserted bone screws,

FIG. 2 is a front view of the intervertebral implant of FIG. 1,

FIG. 3 is a side view of the intervertebral implant of FIG. 1,

FIG. 4 is a top view of the intervertebral implant of FIG. 1,

FIG. 5 is a front view of the intervertebral implant with a front insert, in partial section,

FIG. 6 is a vertical, longitudinal section of the intervertebral implant of FIG. 5, and

FIG. 7 is a horizontal cross-section of the intervertebral implant of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

The intervertebral implant of FIGS. 1 through 4 consists of a 3D structure 10 exhibiting both a convex top side 1 and a convex underside 2, the two sides each being designed to rest against the end plates of two adjacent vertebras. To attain improved anchoring, the top side 1 and the underside 2 may be topographically shaped and be fitted with grooves, ribs or teeth, or their surfaces may be merely roughened.

The 3D implant structure 10 moreover comprises a left side face 3 and a right side face 4, also a front face 5 and a rear face 6. The implant structure 10 also may be hollow and its outer surface may comprise perforations.

The implant structure 10 comprises a plurality of boreholes 9 passing through it and receiving longitudinal affixation elements 20. Preferably four such boreholes 9 shall be provided.

At least one of the boreholes 9 is designed in a way that the longitudinal affixation element 20 received therein may be rigidly connected to the intervertebral implant. The boreholes 9 are conical for that purpose.

Preferably the affixation elements 20 are bone screws having a head 21 and a tip 22. The head 21 conically tapers toward the shank 23, the conicity of the head 21 corresponding to the conicity of the borehole 9. Moreover the four boreholes 9 may be fitted with inner threads 11.

As regards the embodiment variation shown in FIGS. 5 through 7, the 3D structure 10 is fitted at its front face 5 with a preferably metallic insert 8 into which the affixation elements 20 may be anchored. The insert 8 is mounted in vertically displaceable manner in the 3D structure 10.

While the invention has been shown and described herein with reference to particular embodiments, it is to be understood that the various additions, substitutions, or modifications of form, structure, arrangement, proportions, materials, and components and otherwise, used in the practice and which are particularly adapted to specific environments and operative requirements, may be made to the described embodiments without departing from the spirit and scope of the present invention. Accordingly, it should be understood that the embodiments disclosed herein are merely illustrative of the principles of the invention. Various other modifications may be made by those skilled in the art which will embody the principles of the invention and fall within the spirit and the scope thereof. 

1. An intervertebral implant for implantation between an upper vertebra having an upper endplate and a lower vertebra having a lower endplate, the implant comprising: a three dimensional structure having a first lateral side surface, a second lateral side surface, a posterior face, an anterior face, an upper surface and a lower surface, the upper and lower surfaces being sized and configured to contact the upper and lower endplates respectively of the upper and lower vertebra, the three dimensional structure further including at least one groove; a plate having a top surface and a bottom surface, the plate being sized and configured to engage at least one of the first lateral side surface, the second lateral side surface, the posterior face, and the anterior face, the plate also including at least one borehole; wherein the at least one groove of the three dimensional structure and the at least one borehole of the plate are sized and configured to receive at least one bone fixation element; and wherein the at least one bone fixation element includes a head region and a shank region, the shank region being sized and configured for engaging one of the upper and lower vertebra, the groove of the three dimensional structure and the borehole of the plate being sized and configured so that the head region of the bone fixation element does not extend above the upper and lower surfaces of the three dimensional structure.
 2. The intervertebral implant of claim 1, wherein the plate comprises a top surface and a bottom surface, the top and bottom surface of the plate are sized and configured to be entirely contained between the endplates of the upper and lower vertebra when the implant is inserted between the upper and lower vertebra.
 3. The intervertebral implant of claim 2, wherein the head region of the bone fixation element is sized and configured to be entirely contained between the top and bottom surfaces of the plate.
 4. The intervertebral implant of claim 1, wherein the plate is sized and configured to contact the anterior face of the three dimensional structure.
 5. The intervertebral implant of claim 4, wherein the anterior face of the three dimensional structure includes a recess for receiving the plate.
 6. The intervertebral implant of claim 1, wherein the three dimensional structure and the plate are made from different biocompatible materials.
 7. The intervertebral implant of claim 6, wherein the plate is made from a biocompatible metal and the three dimensional structure is made from a biocompatible plastic.
 8. The intervertebral implant of claim 1, wherein the three dimensional structure and the plate are size and configured to be implanted between the upper and lower vertebra as a single unit.
 9. The intervertebral implant of claim 1, wherein the at least one bone fixation element is a bone screw and wherein the at least one borehole formed in the plate is internally threaded and at least a portion of the head region of the bone screw is externally threaded for engaging the internally threaded borehole of the plate.
 10. The intervertebral implant of claim 1, wherein the three dimensional structure further comprises at least one opening, the at least one opening extending from the upper surface to the lower surface.
 11. The intervertebral implant of claim 1, wherein the implant comprises a plurality of boreholes formed in the plate and a plurality of grooves formed in the three dimensional structure, the boreholes and grooves being sized and configured so that the shank region of at least one of the bone fixation element intersects the upper surface of the three dimensional structure and the shank region of another of the at least one bone fixation element intersects the lower surface of the three dimensional structure.
 12. The intervertebral implant of claim 11, wherein the plate further comprises a horizontal center midplane, the plurality of boreholes formed in the plate and the plurality of grooves formed in the three dimensional structure are sized and configured so that the head region of at least one of the bone fixation is located between the top surface of the plate and the horizontal center midplane and the shank region of the bone fixation element intersects the upper surface of the three dimensional body; and wherein the head region of another of the bone fixation element is located between the bottom surface of the plate and the horizontal center midplane and the shank region of the bone fixation element intersects the lower surface of the three dimensional body.
 13. The intervertebral implant of claim 11, wherein the plate further comprises a horizontal center midplane, the plurality of boreholes formed in the plate and the plurality of grooves formed in the three dimensional structure are sized and configured so that the head region of at least one of the bone fixation is located on the horizontal center midplane and the shank region of the bone fixation element intersects the upper surface of the three dimensional body; and wherein the head region of another of the bone fixation element is located on the horizontal center midplane and the shank region of the bone fixation element intersects the lower surface of the three dimensional body.
 14. The intervertebral implant of claim 1, wherein the plate is sized and configured to be slidably displaceable with respect to the three dimensional structure.
 15. The intervertebral implant of claim 1, wherein the three dimensional structure further includes a first height as defined by the upper and lower surfaces of the three dimensional structure and the plate includes a second height as defined by the top and bottom surfaces of the plate, the first height being substantially equal to the second height.
 16. An intervertebral implant for implantation between an upper vertebra having an upper endplate and a lower vertebra having a lower endplate, the implant comprising: a body member, the body member having a first lateral side surface, a second lateral side surface, an anterior face, a posterior face, an upper surface and a lower surface, the upper and lower surfaces of the body member being sized and configured to contact the endplates of the upper and lower vertebra respectively, the body further including a plurality of grooves; and an anterior fixation member, the anterior fixation member being sized and configured to contact the anterior face of the body member, the anterior fixation member having a top surface, a bottom surface and a plurality of boreholes, wherein when the anterior fixation member contacts the anterior face of the body member, the boreholes formed in the anterior fixation member and the grooves formed in the body member are aligned and are sized and configured to receive a plurality of bone fixation elements.
 17. The intervertebral implant of claim 16, wherein the body member further includes a first height as defined by the upper and lower surfaces of the body member and the anterior fixation member includes a second height as defined by the top and bottom surfaces of the anterior fixation member, the first height being substantially equal to the second height.
 18. The intervertebral implant of claim 16, wherein the body member is formed from a first biocompatible material and the anterior fixation member is formed from a second biocompatible material, the second biocompatible material being different than the first biocompatible material.
 19. The intervertebral implant of claim 18, wherein the anterior fixation member is made from a biocompatible metal and the body member is made from a biocompatible plastic.
 20. The intervertebral implant of claim 16, wherein the anterior face of the body member includes a recess for receiving the anterior fixation member.
 21. The intervertebral implant of claim 16, wherein the body member and the anterior fixation member are size and configured to be implanted as a single unit.
 22. The intervertebral implant of claim 16, wherein the at least one bone fixation element is a bone screw, the bone screw comprising a head region and a shank region, the head region being at least partially threaded for engaging an internal thread formed in the borehole of the anterior fixation member.
 23. The intervertebral implant of claim 16, wherein the implant comprises a plurality of grooves formed in the body member and a plurality of boreholes formed in the anterior fixation member, the grooves and the boreholes being sized and configured so that a shank region of at least one of the bone fixation elements intersects the upper surface of the body member and a shank region of another of the at least one bone fixation elements intersects the lower surface of the body member.
 24. The intervertebral implant of claim 23, wherein the anterior fixation member further comprises a horizontal center midplane, the plurality of grooves formed in the body member and the plurality of boreholes formed in the anterior fixation member are sized and configured so that a head region of at least one of the bone fixation elements is located between the top surface of the anterior fixation member and the horizontal center midplane and the shank region of the at least one bone fixation element intersects the upper surface of the body member; and wherein a head region of another of the at least one bone fixation element is located between the bottom surface of the anterior fixation member and the horizontal center midplane and the shank region of the bone fixation element intersects the lower surface of the body member.
 25. The intervertebral implant of claim 16, wherein the anterior fixation member is sized and configured to be slidably displaceable with respect to the body member.
 26. An intervertebral implant for implantation between an upper vertebra having an upper endplate and a lower vertebra having a lower endplate, the implant comprising: a spacer member made from a first material, and having a first side surface, a second side surface, an anterior face, a posterior face, an upper surface, a lower surface and a height defined by the upper and lower surfaces, the upper and lower surfaces being sized and configured to contact the endplates of the upper and lower vertebra; the spacer member having a plurality of grooves; and an anterior plate member made from a second material different from the first material, the anterior plate member being coupled to the anterior face of the spacer member, the anterior plate member having a plurality of boreholes, the plurality of grooves formed in the spacer member being aligned with the plurality of boreholes formed in the anterior plate member for receiving a plurality of bone screws; wherein the anterior plate member includes a top surface, a bottom surface, and a height defined by the top and bottom surfaces, the height of the anterior plate member being substantially the same as the height of the spacer member.
 27. The intervertebral implant of claim 26, wherein the height of the anterior plate member is sized and configured for insertion in-between the endplates of the upper and lower vertebra.
 28. The intervertebral implant of claim 26, wherein the first material is a biocompatible plastic and the second material is a biocompatible metal.
 29. The intervertebral implant of claim 26, wherein the anterior face of the spacer member includes a recess for slidably receiving the anterior plate member.
 30. The intervertebral implant of claim 26, wherein the spacer member and the anterior plate member are size and configured to be implanted as a single unit.
 31. The intervertebral implant of claim 26, wherein the bone screws include a head region and a shank region, the head region being at least partially threaded for engaging an internal thread formed in the borehole of the anterior plate member.
 32. The intervertebral implant of claim 26, wherein the implant comprises a plurality of grooves formed in the spacer member and a plurality of boreholes formed in the anterior plate member, the grooves and the boreholes being sized and configured so that a shank region of one of the bone screws intersects the upper surface of the spacer member and a shank region of another of the bone screws intersects the lower surface of the spacer member.
 33. The intervertebral implant of claim 32, wherein the anterior plate member further comprises a horizontal center midplane, the plurality of grooves formed in the spacer member and the plurality of boreholes formed in the anterior fixation plate are sized and configured so that a head region of one of the bone screws is located between the top surface of the anterior fixation plate and the horizontal center midplane and the shank region of the bone screw intersects the upper surface of the spacer member; and wherein a head region of another of the bone screws is located between the bottom surface of the plate and the horizontal center midplane and a shank region of the bone screw intersects the lower surface of the spacer member.
 34. The intervertebral implant of claim 26, wherein the anterior fixation plate is slidably displaceable with respect to the spacer member so that the anterior fixation plate may move with respect to the spacer member. 